The invention relates to a piston pump for a brake system.
The piston pump of the invention is intended in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS, ASR, FDR and EHB are used for such brake systems. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to pump brake fluid out of a supply container into a wheel brake cylinder or a plurality of wheel brake cylinders (ASR or FDR or EHB). In a brake system with wheel slip control (ABS or ASR) and/or a brake system serving as a steering aid (FDR) and/or an electrohydraulic brake system (EHB), the pump is needed. With the wheel slip control (ABS or ASR), locking of the wheels of the vehicle during a braking event involving strong pressure on the brake pedal (ABS) and/or spinning of the driven wheels of the vehicle in the event of strong pressure on the gas pedal (ASR) can for instance be prevented. In a brake system serving as a steering aid (FDR), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB), in which the pump pumps the brake fluid into the wheel brake cylinder or wheel brake cylinders if an electric brake pedal sensor detects an actuation of the brake pedal, or in which the pump is used to fill a reservoir of the brake system.
One such piston pump is known from German Patent Disclosure DE 40 27 794 A1. The known piston pump has a piston which is guided axially displaceably in a bush that is inserted into a cylinder bore of a pump housing. On one face end of the bush, the cylinder bore is closed by a closure part, which is inserted in pressure-tight fashion into the cylinder bore of the pump housing. Before insertion into the pump housing, the closure part is joined to the bush by crimping, resulting in an easily manipulated preassembled unit that is simple to insert into pump housing. A disadvantage is that the closure part must be joined to the bush in an additional work step.
In the piston pump of the invention, the closure part and the bush are joined together by means of a snap or detent connection. This has the advantage that the bush and the closure part are joined together by simply being put together before insertion into the pump housing. An additional connection operation, for instance crimping as known from the prior art, is dispensed with. The bush and the closure part form an easily manipulated preassembled unit, which can be inserted into the pump housing simply, for instance by press-fitting. Since the connection between the closure part and the bush has only a secondary function, it must hold the closure part on the bush until the piston pump has been inserted into the pump housing; then an approximately aligned orientation of the closure part and the bush suffices, and sealing between the closure part and the bush is unnecessary, so that a snap or detent connection suffices. After insertion into the pump housing, the closure part and the bush are held in a position aligned with one another by the pump housing; sealing exists between the pump housing and the bush, or the closure part. The connection between the closure part and the bush has no further importance once these two parts have been inserted into the pump housing. A snap connection, which can be undone again by pulling the closure part and the bush apart, suffices to connect the closure part to the bush. A detent connection that cannot be done is equally suitable for connecting the closure part to the bush.
Advantageous features and refinements of the invention defined herein are the subject of the invention.